From my experience looking at those graphs, I see that the iorate is pretty low and that the cpu is almost idle. Checking "top", I see that the RAM was sufficient, as there were almost no swap use.
I also use chartbeat.com to see how the users are interacting with the site in realtime. They provide also two useful metrics: user load time and server load time. Looking at those, I can see that the user experience is pretty good, and that the server is up and responding very quickly.
